What causes friction when you rub things together??

Question

Like when you rub your hands.

Answer 1

See the reference, which the first answerer plagiarized.

When you push your hands together, the outermost electrons of your left hand begin to repel the outermost electrons of your right hand. Push harder, and the electrons just push each other out of the way, and the positive nuclei begin to repel each other. Your hands are not smooth at the atomic scale, so the force isn't all normal to the hands. The molecules at the boundary form weak bonds across the boundary. These (mostly bipolar) bonds are much weaker than the covalent bonds among the atoms of one hand, so they are much more easily broken and you can still slide one hand against the other.

Answer 2

Two surfaces rubbing together causes friction. Rubbing your hands together and feeling an intense heat is friction.

Answer 3

Friction is the force of two surfaces in contact, or the force of a medium acting on a moving object (i.e air on an aircraft). It is not a fundamental force, as it is derived from electromagnetic forces between atoms. When contacting surfaces move relative to each other, the friction between the two objects converts kinetic energy into thermal energy, or heat. Friction between solid objects is often referred to as Dry Friction and frictional forces between a solid and fluid (gas or liquid) as Fluid Friction. In addition to these there is also Internal Friction which illustrates a body's ability to recover from external deformation. Contrary to popular belief, sliding friction is not caused by surface roughness, but by chemical bonding between the surfaces. Surface roughness and contact area, however, do affect sliding friction for micro- and nano-scale objects where surface area forces dominate inertial forces.

Static friction
Static friction is the force between two objects that are not moving relative to each other. For example, static friction can prevent an object from sliding down a sloped surface. The coefficient of static friction is typically denoted as μs. It is usually higher than the coefficient of kinetic friction. The initial force to get an object moving is often dominated by static friction...

Another important example of static friction is the force that prevents a car wheel from slipping as it rolls on the ground. Even though the wheel is in motion, the patch of the tire in contact with the ground is stationary relative to the ground, so it is static rather than kinetic friction.

The maximum value of static friction, when motion is impending, is sometimes referred to as limiting friction, although this term is not used universally.


Rolling friction
Rolling friction is the frictional force associated with the rotational movement of a disc or other circular objects along a surface. Generally the frictional force of rolling friction is less than that associated with kinetic friction. Typical values for the coefficient of rolling friction are .001. One of the most common examples of rolling friction is the movement of motor vehicle tires on a roadway, a process which generates heat and sound as by-products.


Kinetic friction
Kinetic (or dynamic) friction occurs when two objects are moving relative to each other and rub together (like a sled on the ground). The coefficient of kinetic friction is typically denoted as μk, and is usually less than the coefficient of static friction. Since friction is exerted in a direction that opposes movement, kinetic friction usually does negative work, typically slowing something down. There are exceptions, however, if the surface itself is under acceleration. One can see this by placing a heavy box on a rug, then pulling on the rug quickly. In this case, the box slides backwards relative to the rug, but moves forward relative to the floor. Thus, the kinetic friction between the box and rug accelerates the box in the same direction that the box moves, doing positive work.

Examples of kinetic friction:

Sliding friction is when two objects are rubbing against each other. Putting a book flat on a desk and moving it around is an example of sliding friction
Fluid friction is the friction between a solid object as it moves through a liquid or a gas. The drag of air on an airplane or of water on a swimmer are two examples of fluid friction.

Fluid Friction
Fluid friction can happen in fluids, or in the air.

Answer 4

rubbing to things together causes friction, if they are both smooth they have less friction than if they are not smooth

Answer 5

Short and Sweet answer- the sticking out molecules scrape against each other.